Filament support for tubular incandescent lamps



Aug. 8, 1967 J. G. CARDWELL. JR 3,335,312

FILAMENT SUPPORT FOR TUBULAR INCANDESCENT LAMPS Filed Jan. 25, 1965 Invent'oT": Johh G. CaTdweLL, J1".

J3 am/ 8 His A b tr'heg nited States Patent 3,335,312 FILAMENT SUPPORT FOR TUBULAR INCANDESCENT LAMPS John G. Cardwell, Jr., Kirtland, Ohio, assignor to General Electric Company, a corporation of New York Filed Jan. 25, 1965, Ser. No. 427,820 3 Claims. '(Cl. 313279) This invention relates generally to electric lamps, and more particularly to incandescent electric lamps of the double-ended type comprising a tubular envelope having a pinch seal at each end through which extend current lead-in conductors connected to respective ends of a helically coiled filament extending longitudinally of the envelope. Still more particularly, the invention relates to a novel support structure for supporting the filament at a point intermediate its ends to maintain its alignment in the tubular envelope, and more especially where the filament is of coiled-coil form, i.e., a helical coil again coiled into a secondary helix.

Whereas certain spiral wire supports and metallic disc supports have been used satisfactorily to support a helical single coil filament from the envelope wall, such supports are not suitable for coiled-coil filaments for such reasons as failure to grip the filament securely or short-circuiting of an inordinate number of coil turns. Special support structureshave also been proposed for use with coiledcoil filaments, again with some shortcomings such as expensive construction or assembly, or looseness due to variations in envelope diameter or loss of springiness :lnder the high temperature conditions prevailing in the amp.

It is therefore an object of the present invention to provide a support structure for double-ended lamps of the type described, especially when provided with helically coiled-coil filaments, although also useful for helically single coiled filaments, and which is of simple construction and will effectively support the filament.

In accordance with one aspect of the invention, the above-mentioned objects are achieved by a simple straight wire support extending longitudinally along the wall of the envelope, having its ends embedded in respective pinch seals at the ends of the envelope, and formed, preferably at its center, with a laterally extending loop portion which firmly encloses a turn of the filament coil at a localized point thereon so that the coil turn extends through the said loop and is supported thereby.

Further features and advantages of the invention will appear from the following detailed description and from the drawing wherein:

FIG. 1 is a side elevation of a lamp comprising the invention;

FIG. 2 is a section along the line II-II in FIG. 1; and

FIG. 3 is a view of the support member in preliminary form before assembly with the filament.

The lamp illustrated in the drawing and specifically described herein may be of the now well-known iodinecycle type disclosed and claimed in Patent 2,883,571 to Fridrich and Wiley. To that end, it comprises a tubular cylindrical envelope 1, preferably of fused silica, or quartz, or the material known as Vycor and comprising 96% silica, having at each end thereof an integral flattened pinch seal 2, which may be of I-shaped cross-section as shown in FIG. 2, and having an intermediate web section 3 and rail sections 4 at its opposite edges. A helically coiled-coil tungsten wire filament 5 extends longitudinally through the interior of the envelope and is connected at respective ends thereof to lead-in conductors 6 having portions thereof hermetically sealed in respective pinch seals 2.

As illustrated herein, the lead-in conductors 6 each comprise an outer lead wire portion 7, of molybdenum for example, having an extremely thin foliated or foil portion 8 which is hermetically sealed within the associated pinch 2. g

The filament 5 terminates in helical single coil leg portions 9 which are closely fitted over tungsten wire spuds or inner lead wire portions 10 which are welded at one end to the foliated portion 8 and which extend into the interior of the envelope 1 within the filament leg 9.

The interior of the envelope 1 contains an inert gas filling such as nitrogen, argon, krypton or xenon at a suitable pressure which may be from several hundred millimeters mercury to several atmospheres, and also a halogen, preferably iodine which maintains the envelope walls free from blackening due to vaporized tungsten from the filament by virtue of the well-known tungsten-iodine regenerative cycle. The envelope may be filled with gas and iodine through an exhaust tube, the sealed residue of which is shown at 11.

In accordance with the present invention, the filament 5 is supported by a straight tungsten wire member 12 which extends longitudinally along the inner wall of the envelope 1 and which has respective ends thereof embedded in the pinch seals 2. A mid-portion of the wire support 12 extends laterally in closed loop form 13 which encloses and firmly embraces a localized point on a single secondary turn of the coiled-coil filament 5 so that said turn extends through the loop 13 and is supported therefrom.

The closed support loop '13 constrains the filament 5 in all directions; the support member 12 is firmly held in both pinches 2 and is insensitive to unavoidable variations in the diameter of commercial tubing from which the envelope 1 is made. Any expansion of the support 12 during operation of the lamp is virtually negligible.

Assembly of the support 12 is facilitated by preliminarily forming it from a single length of wire as shown in FIG. 3 with the right-hand leg thereof at a slight angle to the left-hand leg, as indicated more clearly by its deviation from the broken line extension 14 of the left-hand leg thereof, and by forming the loop 13 in an open U-shape. The support 12 is thereby easily threaded between successive secondary turns of the coiled-coil filament 5 to engage one of said turns within the loop 13; the right-hand leg (FIG. 3) of the wire 12 is then bent up into alignment with the left-hand leg to close the loop 13 upon the filament turn as shown in FIG. 1.

It is also desirable that the ends of the support 12 extend into the respective pinches 2 a limited distance, for example between about one and three or four millimeters. This is especially desirable when the pinch is I-shaped, as shown herein, because of a tendency to form elongated streamers or air pockets upon compression of the envelope walls into the rail sections 4 of the pinch. For the same reason, and also, in the present case, because of difference in coefficients of expansion of the tungsten wire 12 and the silica envelope 1, with resultant lack of a true hermetic seal therebetween, the support wire 12 must not extend through to the exterior of the pinch 2.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric incandescent lamp of the tubular double-ended type comprising a tubular envelope of vitreous material having a pinch seal at each end thereof, a helically coiled wire filament extending longitudinally through the interior of said envelope and connected at respective ends thereof to lead-in conductors hermetically sealed in respective said pinch seals and extending exteriorly thereof, the improvement comprising a filament support in the form of a wire extending longitudinally along the inner wall of said envelope with its ends embedded in respective pinch seals, a mid-portion of said support wire extending laterally in closed loop form enclosing and firmly embracing a localized point on a turn of the coiled filament so that said turn extends through said loop and is supported therefrom.

2. In an electric incandescent lamp of the tubular double-ended type comprising a tubular envelope of vitreous material having a flattened pinch seal at each end thereof, a helically coiled wire filament extending longitudinally through the interior of said envelope and connected at respective ends thereof to lead-in conductors hermetically sealed in respective said pinch seals and extending exteriorly thereof, the improvement comprising a filament support in the form of a wire extending longitudinally along the inner wall of said envelope with its ends embedded in respective pinch seals at corresponding narrow edges thereof at one side of the lamp, a mid-portion of said support wire extending laterally in closed loop form enclosing and firmly embracing a localized point on a turn of the coiled filament so that said turn extendsthrough said loop and is supported therefrom.

3. In an electric incandescent lamp of the tubular double-ended type comprising a tubular envelope of vitreous material having a pinch seal of I-shaped cross-section at 4 each end thereof, a helically coiled wire filament extending longitudinally through the interior of said envelope and connected at respective ends thereof to lead-in conductors hermetically sealed in respective said pinch seals and extending exteriorly thereof, the improvement comprising a filament'support in the form of a wire extending longitudinally along the inner wall of said envelope with its ends embedded in'and terminating within respective corresponding rail portions of the I-shaped pinch seals, :1 mid-portion of said support wire extending laterally in closed loop form enclosing and firmly embracing a localized point on a turn of the coiled filament so that said turn extends through said loop and is supported therefrom.

References Cited UNITED STATES PATENTS 985,422 2/1911 Knight 3 l 3274 3,173,051 3/1965 Berlinghof 313-274 3,270,238 8/1966 Mosby 313-279 JOHN W., HUCKERT, Primary Examiner.

A. I. JAMES, Assistant Examiner. 

1. IN AN ELECTRIC INCANDESCENT LAMP OF THE TUBULAR DOUBLE-ENDED TYPE COMPRISING A TUBULAR ENVELOPE OF VITREOUS MATERIAL HAVING A PINCH SEAL AT EACH END THEREOF, A HELICALLY COILED WIRE FILAMENT EXTENDING LONGITUDINALLY THROUH THE INTERIOR OF SAID ENVELOPE AND CONNECTED AT RESPECTIVE ENDS THEREOF TO LEAD-IN CONDUCTORS HERMETICALLY SEALED IN RESPECTIVE SAID PINCH SEALS AND EXTENDING EXTERIORLY THEREOF, THE IMPROVEMENT COMPRISING A FILAMENT SUPPORT IN THE FORM OF A WIRE EXTENDING LONGITUDINALLY 